Currently, mobile communication service technology can be classified into an asynchronous service environment, used in Europe, and a synchronous service environment, used in North America. Further, as a standard of new mobile communication technology for transmitting packets at high speed, the International Mobile Telecommunications (IMT)-2000 service has been developed around North America and Europe.
The synchronous IMT-2000 service (synchronous mobile communication network) has been developed into Code Division Multiple Access (CDMA) 2000 1x or CDMA 2000 1x Evolution Data Only (EV-DO), and the asynchronous IMT-2000 service (asynchronous mobile communication network) has been developed into Wideband CDMA (WCDMA) Universal Mobile Telecommunications System (UMTS) service. In such a service environment, roaming between synchronous and asynchronous networks has arisen as the biggest outstanding problem. Accordingly, a terminal supporting dual band/dual mode to enable stable roaming between synchronous and asynchronous mobile communication networks is required.
The asynchronous mobile communication network is being constructed in areas having a large number of service requests, so that a synchronous mobile communication network has developed such that the service area thereof includes the service area of the asynchronous mobile communication network. In this environment, when a user moves between an asynchronous mobile communication system and a synchronous mobile communication system, handover between systems is required to provide continuous service. Handover methods for the case where an originating terminal moves from the region of the asynchronous mobile communication network to the region of the synchronous mobile communication network during call origination, and the case where a called terminal moves from the region of the asynchronous mobile communication network to the region of the synchronous mobile communication network during alerting, are required.